Methacrolein (2-methylprop-2-enal; “MA”) is a common intermediate in methacrylic acid (“MAA”) production. MA can be produced from ethylene (C2) feedstock, such as via liquid phase propionaldehyde condensation as disclosed in U.S. Pat. No. 4,496,770. The MA product stream contains methanol that is supplied with formaldehyde that is used in the propionaldehyde condensation. Such methanol can be detrimental in a subsequent oxidation process, which converts MA in the presence of oxygen to MAA in a single step. Thus, a MA stream from conventional processes must be sufficiently free of methanol to be used as a feed stream for a downstream oxidation process, in addition to having a substantial absence of certain impurities (e.g., propionaldehyde, formaldehyde, acetic acid, and organic heavies including, but not limited to, propionic acid, methacrolein dimer, 2-methyl-2-pentenal, and other methacrolein oligomers) that can have a negative effect on efficiency of the oxidation process.
Processes for preparing dry MA have been described in the art. For example, US 2016/0229779 discloses a process comprising (a) providing a wet MA stream containing MA, methanol, and at least 8 weight % water to a phase separator, (b) separating the MA stream into organic and aqueous phases, (c) distilling the organic phase to produce a product stream containing MA and a first overhead stream, (d) sending the first overhead stream back to the phase separator, and (e) distilling the aqueous phase to produce a second overhead stream that is recycled back to the phase separator. The prior art does not, however, disclose a process that further minimizes methanol content in the MA product stream for use in a downstream oxidation process, or further minimizes certain impurities that can negatively affect the efficiency of the oxidation process.
Accordingly, there is a need to develop processes for preparing MA prepared from an ethylene (C2) feedstock, wherein the MA stream has a low methanol content suitable for use in a downstream oxidation process while also removing detrimental impurities.